The present invention relates to a radio receiver of the type having a field intensity detector.
A prior art radio receiver of the type described includes two intermediate frequency (IF) amplifiers connected one after the other. The output of the succeeding IF amplifier is coupled to a frequency discriminator, while the output of the preceding IF amplifier is coupled to a field intensity detector via a junction between the two IF amplifiers. The field intensity detector in turn produces a dc voltage associated with an input field intensity. Of an input field intensity to output voltage relationship of the field intensity detector, a specific part wherein the sensitivity is desirable, i.e., the input field intensity and output voltage are linearly related, is used.
The field intensity detector mentioned above usually comprises a single transistor or diode and, hence, the available range of the linear part is quite narrow. It follows that where a power source voltage is relatively low, the sensitivity to input field intensity is also low limiting the range of the usable field intensities, i.e., dynamic range.